In general, the basic structure of a prior art elliptical fitness machine includes a flywheel, two cranks, and two pedal arms, and a first end of each crank is coaxially connected to the flywheel, and a second end of each crank is pivotally connected to a first end of each corresponding pedal arm, and each pedal arm has a footrest, such that a user can step on the footrest. If the first end of the pedal arm rotates with the crank, the footrest will move in an elliptic path.
Since the elliptical fitness machine provides the function of a striding exercise, the elliptical fitness machine becomes one of the fitness equipments as popular as the treadmill. Traditional elliptical fitness machine does not come with a function of changing the inclination of the machine, and thus users cannot change the level of difficulty of their exercise by changing the inclination of the elliptical fitness machine. U.S. Pat. No. 6,146,313 disclosed a cross training exercise device, and the end of a pedal arm is connected to a guide track for adjusting the height and changing the exercise path of the pedal arm. However, the structure of this machine is not stable enough.
Furthermore, if the elliptical fitness machine and the treadmill are placed flatly on a floor for their use, the footprint of these fitness equipments occupy much area. To reduce the footprint of the fitness machines when the machines are not in use, some treadmills are designed to have a belt frame that can be folded upward, and it is not easy to design a foldable elliptical fitness machine because many mechanisms are disposed on the link rod, and the elliptical fitness machines are usually designed as a partial foldable structure. All of the present elliptical fitness machines do not come with a structure having a variable inclined body. For example, U.S. Pat. No. 6,149,551 only disclosed a foldable elliptical exercise machine that includes one frame, and the frame includes the main components such as a flywheel and a crank to operate with a pedal arm and the track is designed to have a free end which can be turned and folded upright with respect to a second frame. The elliptical exercise machine is partially folded, and the footprint is still large after the machine is folded.